A vehicle operator typically controls acceleration of a vehicle by preselecting transmission shift characteristics, such as by selecting available gear ranges, e.g., FORWARD (F), 3-2-1, and actuating accelerator and brake pedals. Vehicle acceleration is also significantly dependent upon factors including vehicle mass, vehicle load, gradient of the road surface, and others. The rate of acceleration of the vehicle during acceleration and deceleration events is affected by vehicle load, particularly in mass transit, overroad commercial and heavy duty agricultural and construction applications wherein vehicle load may vary over a wide range. For example, a lightly loaded vehicle will exhibit substantially more acceleration than will a fully loaded vehicle for a given throttle pedal depression. Similarly, a lightly loaded vehicle will exhibit substantially more deceleration than will a fully loaded vehicle for a given brake pedal effort. Variations in acceleration and deceleration may affect passenger comfort in mass transit applications. Variations in acceleration and deceleration may affect load stability and shifting in commercial and heavy duty agricultural and construction applications. Variations in acceleration and deceleration may affect vehicle stability in all such applications. This presents operator challenges in that he must constantly be aware of the vehicle loading and road grade factors in an attempt to modulate throttle pedal and brake effort to achieve acceptable acceleration and deceleration.
Furthermore, whereas internal combustion engines provide peak torque relatively high in their operating speed ranges, electric motors provide peak torque in the low end of their speed range. Hybrid powertrains employing electric motors are well known for their low speed torque capabilities. This translates into significant available vehicle launch torque as well as significant available regenerative braking torque. When viewed in light of the undesirability of vehicle thrust variation, the significant low speed torque capabilities of hybrid powertrains presents additional challenges to achieving passenger comfort, load stability and vehicle stability.
What is needed is a method and apparatus to limit acceleration and deceleration of a vehicle to optimize passenger comfort, to minimize effect upon a vehicle load, and improve vehicle stability regardless of variations in acceleration and deceleration affecting factors such as vehicle load and road gradient.